Means for controlling drill bit torque in rotary percussive drilling



' Dec. 14, 1965 J. M. CLEARY MEANS FOR CONTROLLING DRILL BIT TORQUE INROTARY PERGUSSIVE DRILLING Filed NOV. '7, 1962 INVENTOR,

" Cleary M offal- AtiOrney United States Patent This invention has to dowith a means of rotary percussive drilling and, more particularly, tothe reduction of torsional stress during impact of a percussion means.

In rotary percussive drilling, a drill bit or equivalent cutting meansis rotated by suitable surface equipment and the bit is impactedlongitudinally against a formation by suitable percussion means. Indrilling shallow holes, the percussion means may remain at the surfaceand the impact energy is transmitted to the bit by way of a rod or othertubular means which extends from the bit to the surface. In deep welldrilling, the percussion means is usually suspended on a hollow drillstring just above the drill bit.

Normally, that portion of the percussion means which imparts the blow iscalled the hammer, and that part receiving the blow is called the anvilwhich is located on a shank connected to the drill bit. The shank isusually slideably mounted in the percussive unit so that, upon impact,it may move quickly forward driving the drill bit longitudinally againstthe formation. Since the drill bit is to be rotated as it is impacted,the shank is designed to prevent relative rotation between thetelescoping parts of the percussive unit. Prior percussive units haveutilized rigid, nonyielding, torsional drive means such as cooperatingsplines, or keyways and keys, or some other equivalent means thattransmits torque from one telescoping member to another. The telescopingmembers of prior percussive devices are, therefore, rigidly connected toprevent any relative rotational movement between the members. For manyreasons, this adversely affects the operation and reduces the efiiciencyof prior rotary percussive systems. In such systems, when the hammerstrikes the anvil driving the cutters of the drill bit longitudinallyagainst and into the formation, the speed of rotation of the bit isgreatly reduced or stopped completely causing a high torsional shock onthe cutters and creating a torsional shock wave traveling up the drillstring. Before the hammer rebounds for its next blow, the drill stringand drill bit must recover from this shock so that the cutters of thebit are rotated or indexed to a new position for a new bite. If the nextblow of the hammer occurs before the bit is reindexed, the cutters ofthe bit will remain in one position and be driven deeper and deeper intothe formation by succeeding blows.

The above phenomena contribute to such problems as loss of drillingefficiency, excessive wearing and breaking of the cutters, the need forfrequent bit replacement and adjustments to the drilling system, metalfatigue, malfunction of the percussive unit, stuck drill bits, and otherrelated problems.

In view of these problems and the fact that there are many factors whichdetermine a rotary percussive drilling systems effectiveness andeificiency and the relative effect of each factor differs pronouncedlywith the depth, type, and frequency of change of the formation beingdrilled and the design of the bit, drill string, and percussivemechanism, it is extremely diflicult to properly design a rotarypercussive drilling system. In addition, it is often necessary tocompromise the desirable design characteristics of one element of thedrilling system to reduce the effects of shortcomings of anotherelement.

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Accordingly, it is one object of the present invention to provide arotary percussive drilling method and apparatus especially characterizedby its ability to drill effectively and efiiicently through a widevariety of earth formations with maximum drilling rates and minimumsusceptibility to changing drilling conditions.

It is another object of this invention to provide a rotary percussivedrilling system that permits greater freedom in design of the variouselements which affect the efficiency and elfectiveness of a rotarypercussive drilling system.

Still another object of this invention is to provide a percussive earthdrilling unit especially noted for reducing torsional strain on thedrill bit during impact of the hammer and eliminating many of theproblems found in prior rotary percussive drilling devices.

It is still another purpose of this invention to provide a rotarypercussive drilling system that allows the drill string to rotaterelative to the drill bit during impact of the hammer and that suppliesthe necessary rotary driving strength to the drill bit at the desiredmoment after such impact.

Yet another object of this invention is to solve the above problems byproviding a rotary drilling process wherein torsional energy isaccumulated and released at the most opportune moment.

Various other objects and advantages of this invention will appear fromthe following description of this invention together with theaccompanying drawings and appended claims.

In the drawings:

FIGURE 1 is a fragmented, elevational view illustrating a typicalarrangement for a fluid operated percussive earth drilling systememploying this invention.

FIGURE 2 is an elevational, partial, cross-sectional view of apercussive unit having a torque control means embodying the principlesof this invention.

FIGURE 3 is an enlarged transverse, cross-sectional view taken asindicated by 33 on FIGURE 2 and illustrating one embodiment of thetorque control means.

FIGURES 4 and 5 show two alternative embodiments of the torque controlmeans.

The rotary percussive drilling system of this invention is comprised ofrotary means, percussive means, torque control means and drilling means.A system of this type is illustrated in FIGURE 1 wherein drilling means11 is located at the bottom of borehole 13. Above drilling means 11 istorque control means 15 which means is adapted to transmit torque to thedrilling means in a unique way as will be discussed hereafter in moredetail. Communicating with torque control means 15 is percussive means17 which is any means suitable for imparting at time space intervals alongitudinal force to impact drilling means 11 against the bottom ofborehole 13. Preferably, as shown in FIGURE 2, torque control means 15is a part of percussive means 17.

Above percussive means 17 is rotary means 19 which includes rotary drivemeans 21 which is preferably lo cated at the earths surface and whichfor this invention must always be located above torque control means 15.Rotary drive means 21 is any of the many known devices for impartingrotary motion to a drill bit. Rotary means 19 also includes tubularmeans 23 which is commonly termed a drill string or drill rod and formsa flow pas sage for fluid to operate percussive means 17 and to flushdrill cuttings from borehole 13. Tubular means 23 con nects rotary drivemeans 21 to percussive unit 17.

Rotary means 19 must rotate continuously above torque control means 15.Frequently, therefore, it is necessary to increase the angular momentumat the point just above the torque control means by either increasingtherotational speed of rotary drive means 21 or by placing high polarmoment of inertia members at this point, or both. In FIGURE 1, suchmembers are shown by drill collars 25. These drill collars, if employedin the drilling system of this invention, must always be placed abovetorque control means 15 for reasons hereafter made apparent. Preferably,they will be placed immediately above percussive means 17. In accordwith standard drilling practices, components may be taken from or addedto rotary means 19 as long as the rotary means provides the necessarytorsional energy to rotate the drilling means.

To complete the description of a typical rotary earth percussivedrilling system, at the top of tubular means 23 is shown swivel head 27by which the drill string is raised and lowered into the borehole.Associated with swivel head 27 is fluid inlet means 29 which acts as aninlet passage for the flushing and operating fluid. Typically, near thetop of borehole 13 is seal means 31 and fluid outlet means 33 for safelydischarging the flushing and operating fluid from the borehole.

Consider now torque control means 15 in more detail. Torque controlmeans 15 is one of the essential elements of this invention andcooperates with percussive means 17. The torque control means permitsevery component of the drilling system above the torque control means toundergo rotational movement relative to drilling means 11 over theentire interval during which percussive means 17 applies itslongitudinal or axial force to the drilling means. The amount ofrelative rotational movement must be limited as hereafter set forth andthe specific design of torque control means 15 will depend on theparticular percussive unit being employed since the duration of theimpact force or the internal of application of this longitudinal forcevaries with different percussion units as does the interval or timebetween successive applica tions of the force. For any given percussiveunit, the maximum amount or angle of relative rotational movementallowed by torque control means 15 must be greater than the distance orangle that the drilling means would normally move during a time periodequal to the interval of application of this longitudinal force and lessthan the angle or distance that the drilling means would normally rotateduring the period between applications of said force. For example, ifthe drilling means were being rotated at 25,200 per minute (70 r.p.m.)and the duration of application of the longitudinal force were 0.001second, the minimum relative rotational movement allowable by the torquecontrol means will exceed 0.42, and if the force were applied twentytimes a second so that the time between such applications were 0.049second, the maximum relative rotational movement allowable by the torquecontrol means will be less than 20.5 8. Preferably, torque control means15 should be able to allow everything above it to rotate for a periodgreater than the duration of the interval of application of thelongitudinal force and less than 0.6 of the time between successivehammer blows or intervals of application of the longitudinal force tothe drilling means. It is also preferred that torque control means 15absorb torsional energy substantially elastically during the period orangle of relative rotational movement of the drilling means to everycomponent above the drilling means so that drilling means 11 willquickly return to its former position relative to rotary means 19 assoon as the torque control means starts accelerating the speed ofrotation of drilling means 11 after each impact of the percussive means.

The location of torque control means 15 above drilling means 11 aifectsthe extent of the benefits derived from its use. The amount ofbeneficial result increases as the torque control means is moved nearerto the drilling means. Torque control means 15 should, therefore, belocated as near to drilling means 11 as is possible, or immediatelyadjacent thereto. The torque control means will generally be within 6feet thereof and preferably should be within 2 feet thereof.

Shown in FIGURES 2 through 5 are specific examples of torque controlmeans 15. To facilitate understanding, only that portion of thepercussive unit containing torque control means 15 is shown in FIGURE 2where shank 35 telescopes in the usual fashion into the housing ofpercussive unit 17. Above the shank represented by reference numeral 37is a typical hammer means for applying periodic longitudinal or axialforces to the shank. The shank is preferably connected to the drill bitor is an integral part thereof. Between the shank and the percussiveunit housing is torque control means 15 which is formed in the followingmanner. Shank 35 has at least one shank keyway or groove 39 whichcorresponds and cooperates with percussive unit groove 41 in percussiveunit 17 to form a cavity. As shown, there are four such cavities or setsof grooves. Into each cavity is inserted means for absorbing torsionalstrain energy elastically for a limited amount of rotational movement ofpercussive unit 17 relative to shank 35 which means in FIG- URES 2 and 3is S-shaped spring 43.

In FIGURE 4, the means for absorbing and storing torsional energy isbent key 45. In FIGURE 5, modified shank groove 3'9 has only half thewidth of percussive unit groove 41. In addition, shank 35' is formedwith at least one Wing-like extension 47 that fits into and occupieshalf of percussive unit groove 41 thereby forming space 49. Space 49 canbe utilized in a number of ways. Space 49 may be filled with an elasticmaterial having the necessary properties, or with a compressible fluid,or with a fluid whose pressure is controlled by communication with otherparts of the drilling system.

Consider now the operation of the above system. Briefly, the process iscomprised of rotating the rotary means, percussive unit, and drillingmeans and periodically applying longitudinal force to the drilling meansto impact it against the bottom of the borehole. During intervals ofapplication of this longitudinal force, every component of the drillingsystem above the torque control means is rotated relative to thedrilling means and between periods of application of the longitudinalforce, the speed of rotation of the drilling means is increased.Preferably, elastic energy is stored during the period when the speed ofrotation of the drilling means is retarded, and every component abovethe torque control means rotates relative thereto. This stored energy isreleased at the desired predetermined moment after application of theforce to increase the speed of rotation of the drilling means and duringthe moments when the drilling means rotates faster than the remainder ofthe drilling system.

Referring now to FIGURE 1, consider the process in more detail. Wit-hdrilling means 11 on the bottom of borehole 13, the drilling system isrotated by rotary means with torque being transferred from percussivemeans 17 to the drilling means by way of torque control means 15 so thatthe bit will normally rotate therewith. At time spaced intervals,percussive means 17 applies a longitudinal force against drilling means11 impacting it against the formation. As the force is applied, thecutters of drilling means 11 are driven into the formation retarding itsrotation. This creates a torsional shock wave in the cutters which istransmittted upward quickly to torque control means 15. Torque controlmeans 15 allows every component of the drilling system above it tocontinue rotation relatively unimpeded. This quickly creates a wave thatreturns to the drilling means to counterbalance and relieve anytorsional shock strain energy on the drill cutters. When thelongitudinal force applied by the percussion means ceases and before thenext interval of application of a similar force, the speed of rotationof the drilling means is increased and the bit is indexed for a newbite. The amount of relative rotational movement allowed is greater thanthe duration of the longitudinal force and less than the time betweensuccessive blows, and preferably less than 0.6 of this time. Inaddition, preferably, during this period of relative rotational movementwhile the speed of the drill bit is retarded, torsional energy isabsorbed and stored substantially elastically in torque control means15, and this elastic energy is released when the speed of the drillingmeans is increased. This enables the drilling means to rotate fasterthan components above the torque control means and recover its positionrelative to these components before the force is reapplied.

It is understood that various changes in the details, materials, steps,and arrangement of parts, which have been herein described andillustrated in order to explain the nature of this invention, may bemade Within the principle and scope of this invention.

I claim:

1. In a rotary percussive earth drilling system wherein a drilling meansis rotated by a rotary means and is impacted against an earth formationby a periodic longitudinal force applied by a percussive means, theimprovement comprising torque control means between said drilling meansand said rotary means and adapted to allow limited rotational movementof every component of said drilling system above said torque controlmeans relative to said drilling means when said longitudinal force isapplied by said percussive means, said limited rotational movement beinggreater than the angle that said drilling means would normally rotateduring an interval equal to the interval of application of saidlongitudinal force and less than the angle that said drilling meanswould normally rotate during the period between applications of saidlongitudinal force, and said torque control means adapted to cause saiddrilling means to recover its position relative to every component ofsaid drilling system above said torque control means during the periodbetween applications of said longitudinal force.

2. The improvement of claim 1 wherein the torque control means islocated within 6 feet of the cutters of the drilling means.

3. The improvement of claim 1 wherein the torque control means isadapted to absorb torsional energy substantially elastically during theinterval of said relative rotational movement.

4. The improvement of claim 1 wherein the limited rotational movement isgreater than the angle that said drilling means would normally rotateduring an interval equal to the interval of application of saidlongitudinal force and less than 0.6 of the angle that said drillingmeans would normally rotate during the period between applications ofsaid longitudinal force.

5. A rotary percussive drilling system comprising in combination earthdrilling means, percussive means adapted to impart a longitudinal forceat time separated intervals to said drilling means, rotary drive meansadapted to rotate said drilling means and said percussive means, torquecontrol means between said drilling means and said rotary drive meansand adapted to allow limited rotational movement of every component ofsaid drilling system above said torque control means relative to saiddrilling means during said intervals when said longitudinal force isimparted to said drilling means therefor, said limited rotationalmovement being greater than the angle that said drilling means wouldnormally rotate during a period equal to said interval of application ofsaid longitudinal force and less than the angle that said drilling meanswould normally rotate during the period between applications of saidlongitudinal force, and said torque control means adapted to cause saiddrilling means to recover its position relative to every component ofsaid drilling system above said torque control means during the periodbetween applications of said longitudinal force.

6. The drilling system of claim 5 wherein the torque control means islocated within 6 feet of the cutters of the drilling means.

7. The drilling system of claim 5 wherein the torque control means isadapted to absorb torsional energy substantially elastically during theinterval of said relative rotational movement.

8. The drilling system of claim 5 wherein the limited rotationalmovement is greater than the angle that said drilling means wouldnormally rotate during a period equal to said interval of application ofsaid longitudinal force and less than 0.6 of the angle that saiddrilling means would normally rotate during the period betweenapplications of said longitudinal force.

References Cited by the Examiner UNITED STATES PATENTS 2,325,132 7/ 1943Haushalter -56 2,825,534 3/1958 Reid 175-405 2,911,192 11/1959 Bouoher175-56 3,033,011 5/1962 Garrett 175-320 X CHARLES E. OCONNELL, PrimaryExaminer.

BENJAMIN BENDE'IT, Examiner.

5. A ROTARY PERCUSSIVE DRILLING SYSTEM COMPRISING IN COMBINATION EARTHDRILLING MEANS, PERCUSSIVE MEANS ADAPTED TO IMPART A LONGITUDINAL FORCEAT TIME SEPARATED INTERVALS TO SAID DRILLING MEANS, ROTARY DRIVE MEANSADAPTED TO ROTATE SAID DRILLING MEANS AND SAID PERCUSSIVE MEANS, TORQUECONTROL MEANS BETWEEN SAID DRILLING MEANS AND SAID ROTARY DRIVE MEANSAND ADAPTED TO ALLOW LIMITED ROTATIONAL MOVEMENT OF EVERY COMPONENT OFSAID DRILLING SYSTEM ABOVE SAID TORQUE CONTROL MEANS RELATIVE TO SAIDDRILLING MEANS DURING SAID INTERVALS WHEN SAID LONGITUDINAL FORCE ISIMPARTED TO SAID DRILLING MEANS THEREFOR, SAID LIMITED ROTATIONALMOVEMENT BEING GREATER THAN THE ANGLE THAT SAID DRILLING MEANS WOULDNORMALLY ROTATE DURING A PERIOD EQUAL TO SAID INTERVAL OF APPLICATION OFSAID LONGITUDINAL FORCE AND LESS THAN THE ANGLE THAT SAID DRILLING MEANSWOULD NORMALLY ROTATE DURING THE PERIOD BETWEEN APPLICATIONS OF SAIDLONGITUDINAL FORCE, AND SAID TORQUE CONTROL MEANS ADAPTED TO CAUSE SAIDDRILLING MEANS TO RECOVER ITS POSITION RELATIVE TO EVERY COMPONENT OFSAID DRILLING SYSTEM ABOVE SAID TORQUE CONTROL MEANS DURING THE PERIODBETWEEN APPLICATIONS OF SAID LONGITUDINAL FORCE.